#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>

int main()
{
    double r, R, mid = 0.0;
    scanf("%lf %lf", &r, &R);
    mid = (1.0 / r) + (1.0 / R);
    printf("%.2lf", 1.0 / mid);
    return 0;
}